U.S. patent application number 11/053482 was filed with the patent office on 2006-08-10 for riser termination device.
This patent application is currently assigned to Stone & Webster Process Technology, Inc.. Invention is credited to Jim Evans, John Hood, Gary Jackson, Warren Letzsch, Ed Yuan.
Application Number | 20060177357 11/053482 |
Document ID | / |
Family ID | 36780148 |
Filed Date | 2006-08-10 |
United States Patent
Application |
20060177357 |
Kind Code |
A1 |
Yuan; Ed ; et al. |
August 10, 2006 |
Riser termination device
Abstract
The present invention provides an improved separator for use in
hydrocarbon cracking process.
Inventors: |
Yuan; Ed; (Houston, TX)
; Letzsch; Warren; (Ellicott City, MD) ; Jackson;
Gary; (Katy, TX) ; Evans; Jim; (US) ;
Hood; John; (Harper, TX) |
Correspondence
Address: |
HEDMAN & COSTIGAN P.C.
1185 AVENUE OF THE AMERICAS
NEW YORK
NY
10036
US
|
Assignee: |
Stone & Webster Process
Technology, Inc.
|
Family ID: |
36780148 |
Appl. No.: |
11/053482 |
Filed: |
February 8, 2005 |
Current U.S.
Class: |
422/147 ;
422/139; 422/145 |
Current CPC
Class: |
B01J 8/18 20130101; C10G
11/187 20130101; B01D 45/16 20130101; B01J 8/005 20130101; B01J
8/0055 20130101; B01D 45/06 20130101; C10G 11/18 20130101 |
Class at
Publication: |
422/147 ;
422/139; 422/145 |
International
Class: |
B01J 8/18 20060101
B01J008/18; B32B 27/04 20060101 B32B027/04 |
Claims
1. A solids-vapor separation device comprising: (1) an inlet
portion for receiving a mixed stream of solids and vapors; (2) a
turning portion for imparting a centrifugal motion onto said solids
and said vapors comprising a semi-circular ceiling and a
semi-circular floor; (3) a vertical portion for receiving said
turned solids and said vapors and wherein a majority of the vapors
with some entrained solids are separated from the majority of the
solids; (4) an angular ledge for receiving the majority of the
solids, allowing for compaction of the solids and facilitating
further separation of vapors; (5) a vapor outlet for receiving the
separated vapors with any entrained solids from the vertical
portion and the angular ledge located below said semi-circular
floor; and (6) a dipleg for receiving solids from the angular
ledge.
2. A device as defined in claim 1 wherein said device is a riser
termination device, said vapors comprise cracked product vapors and
said solids comprise spent particulate solids.
3. A device as defined in claim 1 further comprising a baffle
located above said angular ledge, below said vapor outlet and
tangential to said vapor outlet, whereby a slot is formed between a
bottom portion of the baffle and said angular ledge and a vapor
conduit is formed between an upper portion of said baffle and said
semi-circular floor.
4. A device as defined in claim 1 wherein said dipleg is sealed
with a bathtub sealing means.
5. A device as defined in claim 1 where in said dipleg is sealed in
a fluidized bed of particulate solids.
6. A cracking apparatus comprising: (a) a disengaging vessel
comprising an upper dilute zone and a lower dense zone; (b) a riser
reactor for cracking a hydrocarbon feedstock in the presence of hot
particulate solids, said riser reactor having an outlet for
producing a riser effluent comprising spent solids and cracked
product vapors; and (c) a separation device comprising: (i) an
inlet for receiving the riser effluent; (ii) a turning zone for
imparting centrifugal force onto the riser effluent, said turning
zone comprising a curved ceiling and curved floor; (iii) a vertical
zone for receiving effluent from the turning zone; said vertical
zone allowing for a majority of said spent solids to separate from
the majority of said cracked product vapors as a result of the
centrifugal force provided by said turning zone; (iv) an angled
ledge for receiving the majority of said spent solids from said
vertical zone and allowing for compaction of said spent solids and
further separation of cracked product from said spent solids; (v) a
dipleg for receiving the spent solids from said angled ledge and
for delivering said spent solids to a fluidized zone; and (vi) a
vapor outlet for receiving cracked product vapors from said
vertical zone and said angled ledge and delivering said cracked
product vapors to the upper dilute zone of said disengaging
vessel.
7. A cracking apparatus as defined in claim 6 wherein said cracking
apparatus is a catalytic cracking apparatus and said hot
particulate solids comprise cracking catalyst.
8. A cracking apparatus as defined in claim 6 wherein said cracking
apparatus is a thermal particulate cracking apparatus and said hot
particulate solids comprising substantially inert particulates.
9. A cracking apparatus as defined in claim 6 wherein said
separation device further comprising a baffle located above said
angular ledge, below said vapor outlet and tangential to said vapor
outlet, whereby a slot is formed between a bottom portion of the
baffle and said angular ledge and a vapor conduit is formed between
an upper portion of said baffle and said semi-circular floor.
10. A cracking apparatus as defined in claim 6 wherein said riser
reactor is provided with a transition zone at the top of said riser
reactor.
11. A cracking apparatus as defined in claim 10 wherein said
transition zone modifies the shape of the cross section from a
substantially circular shape in the reactor to a substantially
rectangular or square shape at the inlet to said separation
device.
12. A cracking apparatus as defined in claim 10 wherein said
transition zone provides a gradual reduction in the cross section
of said riser reactor to said inlet to said separation zone.
13. A cracking apparatus as defined in claim 6 wherein said
cracking apparatus comprises two or more of said separation
devices.
14. A cracking apparatus as defined in claim 13 wherein said
separation device further comprises a wall that extends into the
top of said riser reactor for splitting the flow into each of said
separation devices.
15. A cracking apparatus as defined in claim 14 wherein there are
two separation devices and said wall is wedge-shaped.
16. A cracking apparatus as defined in claim 14 wherein there are
three separation devices and said wall has a triangular
cross-section.
17. A cracking apparatus as defined in claim 6 wherein said dipleg
is sealed with a bathtub sealing means.
18. A cracking apparatus as defined in claim 6 wherein said dipleg
is sealed in a fluidized bed of particulate solids located in said
dense bed of said disengaging vessel.
19. A cracking apparatus as defined in claim 17 wherein said
bathtub sealing means is fluidized with a stripping gas.
20. A cracking apparatus as defined in claim 6 further comprising a
quenching means located to quench cracked product vapors in said
vapor product outlet.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to the field of gas-solid
separation devices, such as, but not limited to, riser termination
devices and, more particularly, to the field of separating mixed
phase gas-solid streams in hydrocarbon cracking units.
BACKGROUND OF THE INVENTION
[0002] Chemical reaction systems utilizing solids in contact with
gaseous or vaporized feedstocks long have been employed in the art.
The solids may participate in the reaction as a catalyst; provide
heat required for an endothermic reaction; or both. Alternatively,
the solids may provide a heat sink required for an exothermic
reaction. The terms "solid" and "catalyst" are used interchangeably
herein. Similarly, the terms "gas" and "vapors" are used
interchangeably herein.
[0003] In the past, cracking of petroleum products was performed in
fluidized bed reactors that had as an advantage a relatively
isothermic temperature profile. However, as catalysts improved and
reaction residence times decreased, the bed depth became shallower
and increasingly unstable. For this reason, tubular reactors
employing solid-gas contact in pneumatic flow were developed and
have been used with great success, particularly in the catalytic
cracking of hydrocarbons to produce gasoline products where reactor
residence time ranges from about 0.5 to about 5 seconds, preferably
less than about 2 seconds.
[0004] In general, catalytic cracking of relatively high boiling
hydrocarbons to form substantial quantities of material boiling in
the gasoline range is carried out in the following sequence as
described in Pfeiffer et al., U.S. Pat. No. 4,756,886, which is
incorporated herein by reference: hot regenerated catalyst is
contacted with a hydrocarbon feed in a reaction zone under
conditions suitable for cracking; the cracked hydrocarbon gases are
separated from the spent catalyst using conventional cyclones and
the spent catalyst is steam stripped to remove volatile
hydrocarbons and subsequently fed to a regeneration chamber where a
controlled volume of air is introduced to burn the carbonaceous
deposits from the catalyst, and the regenerated catalyst is
returned to the reaction zone.
[0005] A problem with these fluidized catalytic cracking systems
has been obtaining rapid and efficient separation of the gas and
solid phases in order to cease the catalytic cracking and thereby
prevent overcracking to less desirable by-products.
[0006] Previous attempts have been made in the art to separate the
phases by use of centrifugal force and/or deflection means. For
example, Nicholson, U.S. Pat. No. 2,737,479, combines reaction and
separation steps within a helically wound conduit containing a
plurality of complete turns and having product draw-offs on the
inside surface of the conduit to separate solids from the gas phase
by centrifugal force. Solids accumulate on the outside of the
conduit, while gases concentrate at the inner wall, and are removed
at the draw-offs. The Nicholson unit produces a series of gas
product streams each in a different stage of feed conversion due to
the multiple product draw offs that cause varying exposure time of
the gas to the reaction conditions.
[0007] Ross et al., U.S. Pat. No. 2,878,891, attempted to overcome
this defect by appending to a standard riser a modification of
Nicholson's separator. Ross et al. '891 teaches a separator
comprised of a curvilinear conduit making separation through a
180.degree. to 240.degree. turn. Centrifugal force directs the
heavier solids to the outside wall of the conduit allowing gases
that accumulate at the inside wall to be withdrawn through a single
drawoff. While the problem of various stages of conversion of the
product is decreased, other drawbacks of the Nicholson unit are not
eliminated.
[0008] Both devices effect separation of gas from solids by
changing the direction of the gas 90.degree. at the withdrawal
point, while allowing solids to flow linearly to the separator
outlet. Because solids do not undergo a directional change at the
point of separation, substantial quantities of gas flow past the
withdrawal point to the solids outlet. For this reason, both
devices require a conventional separator at the solids outlet to
remove excess gas from the solid particles. However, product gas
removed in the conventional separator has remained in intimate
contact with the solids, and, therefore, may be degraded.
[0009] Another drawback of these devices is the limitation on
scale-up to commercial size. As conduit diameter increases, the
path traveled by the mixed phase stream increases proportionately
so that large diameter units have separator residence times
approaching those of conventional cyclones. Increasing velocity can
increase residence time, but as velocities exceed 60 to 75 ft/sec,
erosion by particles impinging along the entire length of the
curvilinear path progressively worsens. Reduction of the flow path
length by decreasing the radius of curvature of the conduit also
reduces residence time, but increases the angle of impact of solids
against the wall, thereby accelerating erosion.
[0010] Pappas, U.S. Pat. No. 3,074,878, devised a low residence
time separator using deflection means wherein the solid gas stream
flowing in a tubular conduit impinges upon a deflector plate
causing the solids, which have greater inertia, to be projected
away from a laterally disposed gas withdrawal conduit located
beneath said deflector plate. Because solids do not change
direction while the gas phase changes direction relative to the
inlet stream by only 90.degree. there results an inherently high
entrainment of solids in the effluent gas. While baffles placed
across the withdrawal conduit reduce entrainment, these baffles as
well as the deflector plate are subject to very rapid erosion in
severe operating conditions of high temperature and high velocity.
Thus, many of the benefits of the separators of the prior art are
illusory because of the limitations in their efficiency, operable
range and scale up potential.
[0011] Gartside et al., U.S. Pat. Nos. 4,288,235, 4,348,364 and
4,433,984, disclosed an apparatus for rapidly separating
particulate solids from a mixed phase solids-gas stream from
tubular type reactors. The Gartside apparatus projects solids by
centrifugal force against a bed of solids as the gas phase makes a
180.degree. directional change to effect separation. The solids
phase, however, is required to undergo two 90.degree. changes
before exiting the apparatus.
[0012] Larson, U.S. Pat. No. 3,835,029, discloses a downflow
catalytic cracker entering a cylindrical separator with a series of
openings in the outside wall through which the hydrocarbon passes.
The catalyst solids pass downwardly to a stripper section and then
into a regenerator. Within the equipment and spatial constraints,
the separator of Larson is limited because there is no
progressively increasing lateral flow path as a function of the
height of the openings to help effectuate separation once the mixed
phase gas solids stream enters the separator.
[0013] Pfeiffer, U.S. Pat. No. 4,756,886, teaches a rough cut
separator that has a frusto-conical chamber having substantially
conical walls tapering downwardly and outwardly and means defining
at least one opening in said conical walls for conveying solids
free gas.
[0014] Other more recent globe-type separators are disclosed in
Barnes, U.S. Pat. No. 4,666,674 and Van der Akker et al., U.S. Pat.
No. 4,961,863. These references teach the use of a spherical-shaped
separator with a tangential entry to reduce pressure drops in the
separator.
[0015] Special mention is made of Ross, Jr. et al., U.S. Pat. No.
5,837,129, which discloses the original ramshorn-type separator.
The Ross, Jr. et al. '129 patent, teaches that employing an
inertial type separator at the terminal end of a riser reactor in
combination with a horizontally disposed gas oulet with the
horizontally disposed gas outlet facing upwardly and toward the
riser reactor or upwardly and away from the riser reactor provides
a quick and efficient separation of hydrocarbon vapor product from
catalyst particles, thereby reducing the post riser reactor contact
time between the vapor product and catalyst particles and reducing
the post reactor thermal cracking.
[0016] Another useful separator is disclosed in Gauthier et al.,
U.S. Pat. No. 6,113,777, which discloses a direct turn separator
for use in fluidized bed thermal cracking or catalytic cracking,
also known as a linear disengaging device or LD.sup.2. This
separator, although providing significant advantages, has proved
difficult to operate in a sealed dipleg mode.
[0017] Although these separation devices have met with some
success, there still exists a need in the art for more improved
devices, especially an improved linear disengaging device that can
operated in a sealed dipleg mode, with improved solid separation
efficiency, reduced vapor underflow from the dipleg and wherein
pre-stripping can be provided.
SUMMARY OF THE PRESENT INVENTION
[0018] It is an object of the present invention to provide an
improved gas-solids separation device.
[0019] It is another object of the present invention to provide a
gas-solids separation device with improved ability to operate in a
sealed dipleg mode.
[0020] It is a further object of the present invention to provide a
gas-solids separation device that can provide pre-stripping.
[0021] It is still another object of the present invention to
provide a gas-solids separation device that reduces vapor underflow
from the dipleg.
[0022] It is still a further object of the present invention to
provide an improved gas-solids separation device that is useful in
catalytic cracking operations.
[0023] It is yet a further object of the present invention to
provide an improved gas-solids separation device that is useful in
riser catalytic cracking.
[0024] It is yet another object of the present invention to provide
an improved gas-solids separation device that is useful in thermal
particulate cracking operations.
[0025] Accordingly, such an improved riser termination device is
provided by the present invention. The device of the present
invention comprises: (1) an inlet portion for receiving spent
solids and cracked product vapors, (2) a turning portion for
imparting a centrifugal motion onto said spent solids and cracked
product vapors; (3) a vertical portion for receiving the turned
spent solids and cracked product vapors and wherein a majority of
the vapors with some entrained solids are separated from the
majority of the solids; (4) an angular ledge for receiving the
majority of the solids, allowing for compaction of the solids and
facilitating further separation of vapors; (5) a vapor outlet for
receiving the separated vapors with any entrained solids from the
vertical portion and the angular ledge; and (6) a dipleg for
receiving solids from the angular ledge. In a preferred embodiment,
a baffle is provided at a point tangential to and below the vapor
outlet, and above the angular ledge to provide a slot between the
bottom of the baffle and the angular ledge for passage of the
solids, and a gap at the top of the baffle for allowing passage of
the vapor separated in the vertical portion.
[0026] These and other objects of the invention will be apparent to
those of ordinary skill in the art from an inspection of the
specification, figures and claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] FIG. 1 is depicts a preferred separator of the present
invention.
[0028] FIG. 2 depicts a preferred separator of the present
invention in a riser cracking apparatus.
DETAILED DESCRIPTION AND DESCRIPTION OF THE PREFERRED
EMBODIMENTS
[0029] FIG. 1 is a partial cutaway view showing a separator 2 of
the present invention. Separator 2 comprises two separating
portions 4 centrally positioned atop a riser reactor 6 and
separated by a separating wall 8 (see FIG. 2) that extends into the
riser reactor 6. Each separating portion 4 is comprised of a
semi-circular roof 10, a vertical outside side wall 12, a vertical
interior wall 14, a front vertical wall 16, a back vertical wall
(not shown), a dipleg 18 and an angled side wall portion 20
connecting vertical outside wall 12 to the dipleg 18. Attached to
the front and back vertical walls are gas conduits 22. The bottom
of the gas conduit 22 is contiguous with semicircular baffle 24
that extends through the separator 2 leaving an open space 26 below
the semicircular portion 24. Attached to the interior of the front
and back vertical walls and below the open space is a baffle 28.
The baffle 28 is located above the angled side wall portion 20 to
leave a gap 30 and is positioned tangential to the outside of
semicircular baffle 24. The diplegs 18 extend into a bathtub
sealing means 32. Bathtub sealing means 32 is provided with
fluidization nozzles 35 and overflow slots 36. Preferably,
fluidization nozzles 35 fluidize the particular solids with a
stripping gas, such as steam or other stripping gas known to those
skilled in the art.
[0030] Referring now to FIG. 2, there is shown a separator of the
present invention in the context of a riser reactor 6 that extends
centrally into a disengaging vessel 34. Of course, the present
invention would have equal applicability to a riser reactor that
was external to the disengaging vessel, as will be appreciated by
those of ordinary skill in the art. See, e.g., Forgac et al., U.S.
Pat. No. 5,043,058. Cracked product and spent catalyst travel
upwardly through riser reactor 6. At the top of the riser 6, the
cracked product and spent catalyst flow is divided by a
wedge-shaped riser separator wall 8. In an embodiment where there
is only one separator, there would be no need for the riser
separator wall 8. In embodiments where there are three or more
separators on top of the riser, the separator wall 8 will take on
the shape of a triangular wall and the like.
[0031] The top of the riser 6 may be provided with a transition
zone 6A as described in U.S. Pat. No. 6,113,777, in which the cross
section at the top of the riser is modified, such as being tapered
to form a narrowing section, which accelerates the particle mixture
between the upper portion of the riser reactor and the separator.
The transition zone 6A can have the following functions: [0032] (1)
it can modify the shape of the cross section that passes from a
substantially circular shape in the reactor to a substantially
rectangular or square shape at the inlet to the separator. This
rectangular cross section can have a ratio of 1 to 3 between the
longest side and the shortest side, the shortest side generally
being that which turns about the gas outlet. [0033] (2) It can
accelerate the flow to an improved separation velocity by means of
a gradual reduction in the cross section in the separator.
Preferably the outlet cross section or, in the case where there is
a plurality of separators, the sum of the outlet cross sections
from the transition zone of each separator can be in the range of
0.5 to one in the cross section of the reactor. Under these
conditions, the velocity in the rectangular cross section generally
is in the range of from about 10 to about 30 m/s, preferably from
about 15 to about 25 m/s, while it is, for example from about 10 to
about 25 m/s in the cylindrical cross section of the reactor. The
length of the transition zone can be in the range of from about 0.1
to about 10 times the reactor diameter, more preferably from about
0.5 to about 3 times the reactor diameter.
[0034] The cracked product and spent catalyst flow enter separator
4 and is then turned centrifugally by an upper semicircular wall 10
and baffle 24. This semicircular portion of the separator, or
turning zone, is adapted to rotate the mixture in a vertical plane
through an angle, which is less than 360.degree., preferably in the
range of from about 70.degree. to about 225.degree., and most
preferably about 180.degree.. Due to centrifugal forces, the
majority of the spent catalyst follows the semicircular contour of
upper semicircular wall 10, vertical sidewall 12 and angled
sidewall 20. The degree of angle between vertical sidewall 12 and
angled sidewall 20 should be such that the spent catalyst easily
can slide down the angled sidewall 20, but preferably ranges
between about 10.degree. and about 60.degree.. The spent catalyst
slides down the angled sidewall 20 (or ledge) and under baffle 28
through slot 30. The baffle 28 is located approximately tangential
to the outside of tube opening 26 and the end of baffle 24. The
baffle 28 encourages solid and gas separation by causing compaction
of the solids at slot 30. Baffle 28 is constructed of a material
that is resistant to abrasion and high temperatures, as is known to
those skilled in the art. The gap between the bottom of the baffle
28 and angled sidewall 20 preferably ranges from about 6 inches to
about 4 feet and the gap between the top of the baffle 28 and the
bottom of the tube opening 26 preferably ranges from about 6 inches
to about 5 feet.
[0035] After passing through slot 30, the spent catalyst exits the
separator 4 via a dipleg 18, which generally may have either a
circular or rectangular cross-section. The dipleg 18 for use in the
present invention must have an open bottom, preferably with no
design that restricts solid flow exiting the dipleg 18. In FIG. 2,
dipleg 18 is sealed with a bathtub sealing means, which is
fluidized. A complete description of bath tub sealing means that
are useful in the practice of the present invention is disclosed in
commonly assigned U.S. Pat. No. 6,692,552. Steam optionally can be
introduced into the dipleg through a suitable means to provide
pre-stripping and ensure a fluidized standpipe. In the embodiment
of FIG. 2, prestripping also is effected in the bathtub sealing
means 32 by the introduction of steam through nozzles 35 (see FIG.
1). The prestripped catalyst exits the bathtub sealing means 32 by
overflowing out notches 36 located in the top of the sealing means
32. The prestripped catalyst then falls through the lower portion
40 of the upper dilute phase 38 of disengaging vessel 34 and into
the dense fluidized bed 42 for further stripping as is known to
those skilled in the art. A portion of the catalyst entering the
bathtub sealing means 32 may also pass through openings 37 in the
bottom of the bathtub. The dense fluidized bed 42 is fluidized with
stripping medium, preferably steam, via fluidization ring 44.
Optionally, dense fluidized bed 42 may be packed or equipped with
trays (not shown) as is known to those skilled in the art to
facilitate stripping. The stripped catalyst then exits the dense
fluidized bed 42 via a standpipe 46 for regeneration.
[0036] Alternatively, instead of the use of the bath tub sealing
means, dipleg 18 can be sealed by extension directly into dense
fluidized bed 42 located in the bottom portion of disengaging
vessel 34.
[0037] As the centrifugal force forces the solids to the outside of
the separator, the cracked product vapors peel off from the solids,
assisted by baffle 28, and exit the separator above the baffle 28
and below the semicircular portion 24 through opening 26 and into
vapor outlet tube 22. Each semicircular section optionally may be
provided with two vapor outlet tubes, one on each side of the
separator. Additional vapor is removed by compression of the solids
at slot 30, which additional vapor proceeds upwardly through space
48 and into opening 26. Optionally, a quench injection means 51,
such as a nozzle or other spray device known to those skilled in
the art, may be provided in vapor outlet tube 22 to assist in
halting any thermal cracking reactions. Any of the quench liquids
known to those skilled in the art may be employed in the practice
of the present invention, such as, but not limited to those
disclosed in the aforementioned Forgac, U.S. Pat. No. 5,043,058.
Alternatively, a quench injector may be provided to distributed
quench liquid into the upper dilute phase 38 of disengaging vessel
34, such as, for example, in proximity to the vapor outlet port 50.
Cracked product vapors, with some entrained solids, exit vapor
outlet tube 22 through port 50 and proceed into the upper dilute
phase 38 of disengager vessel 34.
[0038] Because the primary purpose of the separation device of the
present invention it to make a rough cut separation of the catalyst
from the cracked product vapors to prevent overcracking, the
separator of the present invention is designed to make a rapid
separation of a majority of the catalyst particles from the cracked
product vapors. As a result, the cracked product vapors leaving the
separator are entrained with a minor portion of catalyst particles
and fines, which require additional separation. Accordingly, the
cracked product vapors with entrained solids are drawn into cyclone
separator 52 via entry opening 54. Additionally, steam and stripped
volatile hydrocarbons exiting the bath tub sealing means (if
present) and the dense catalyst bed 42, with any entrained catalyst
particles, also are drawin into the cyclone separator 52. In
cyclone 52, the entrained solids are separated from the cracked
product vapors. The solids are removed via a dipleg 56 and
delivered to the dense fluidized bed 42. Dipleg 56 in FIG. 2 is
depicted as unsealed and extending into bed 42, but other
arrangements known to those skilled in the art may be employed,
such as a sealed dipleg and/or a dipleg that does not extend into
bed 42. The cracked product vapors are removed from cyclone 52 via
product vapor line 58 and exit the disengager vessel for downstream
processing. Although only one cyclone is shown in FIG. 2, it will
be appreciated by those skilled in the art and multiple cyclones
may be employed to effect the final separation.
[0039] The above-mentioned patents are all hereby incorporated by
reference.
[0040] Many variations of the present invention will suggest
themselves to those skilled in the art in light of the
above-detailed description. One such option would close couple the
outlet tubes 22 to the secondary cyclones 52. This and all such
obvious variations are within the full-intended scope of the
appended claims.
* * * * *